JP3066947B2 - Sensor circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensor circuit for detecting a detection quantity to be measured as modulation of a reference light, and more particularly to a sensor circuit in which the reference light is stabilized.

[0002]

2. Description of the Related Art Conventionally, as this type of sensor circuit, there is, for example, a current sensor circuit used in a current measuring section of an electronic integrated watt-hour meter for measuring a transaction power amount.

FIG. 3 is a block diagram showing a configuration of the current sensor circuit. DC reference light is emitted from a light emitting diode (LED) 1 to an optical current sensor 3 via an optical fiber 2. The photocurrent sensor 3 detects the amount of current flowing through a drawing wire (not shown) based on the strength of a magnetic field generated by the current, and modulates the irradiated reference light according to the detected current amount. In other words, the photocurrent sensor 3 increases and outputs the amount of reference light when the detected current amount is large, and decreases and outputs the reference light amount when the detected current amount is small. The reference light thus modulated is applied to the optical fiber 4
To the photosensor 5, and the photosensor 5 photoelectrically converts the received optical signal into a current Ip. This current I
p is composed of a DC component corresponding to the DC reference light and an AC component generated by modulation by the photocurrent sensor 3. This AC component corresponds to the detected amount, that is, the measured current amount.

A current subtraction circuit 6 subtracts a DC current component (Iref-Iα) corresponding to most of the DC reference light from the output current Ip of the photosensor 5. The reason why the DC current component Iref corresponding to all of the DC reference light is not subtracted is that a predetermined DC current component Iα is fed back to keep the light amount of the reference light irradiated on the photocurrent sensor 3 constant.
The subtracted current is converted into a voltage signal by a current / voltage converter 7 and output to a multiplier (not shown) as a sensing voltage Vs. The multiplier multiplies the voltage value measured by the voltage measurement unit of the electronic watt-hour meter by the voltage value output from the current / voltage converter 7 to calculate the power consumption. Further, the output of the current / voltage converter 7 is also supplied to a low-pass filter 8, and in this low-pass filter 8,
A direct current (DC) voltage component Voff included in the sensing voltage Vs is extracted. This DC voltage component Voff corresponds to the above-described DC current component Iα, and is converted again by the voltage / current converter 9 into the current Ioff. The LED 1 is driven by the current Ioff corresponding to the DC voltage component Voff, and emits DC reference light.

In such a sensor circuit, the LED 1
If the light amount of the DC reference light applied to the photocurrent sensor 3 fluctuates for some reason, this fluctuation appears as a change in the DC voltage component Voff in the sensing voltage Vs, and is taken out by the low-pass filter 8. This D
Due to the change in the C voltage component Voff, the LED drive current Ioff generated in the voltage / current converter 9 is feedback-controlled, and the amount of light emitted from the LED 1 to the photocurrent sensor 3 is always kept at a constant amount. That is, in this sensor circuit, the DC component of the reference light forms a feedback loop.

[0006]

However, in the above-mentioned conventional sensor circuit, the DC component of the reference light that feeds back the closed loop appears as a DC voltage component Voff in the sensing voltage output of the current / voltage converter 7. . Although this DC voltage component Voff is originally a small value, this DC voltage component Voff is applied to the sensing voltage output to the multiplier.
When the voltage component Voff is superimposed, it causes a measurement error in the measured power amount. For example, in the low current range of the detection current, the DC voltage component V
Off occupies a higher proportion, causing measurement errors. For this reason, the conventional sensor circuit is not suitable for an electronic watt-hour meter which is required to have a capability of measuring a current with high accuracy over a wide dynamic range.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a light-emitting means for emitting a DC reference light, and a modulation according to an amount of detection of the irradiated DC reference light. A photoelectric conversion means for converting an optical signal modulated by the detection means into an electric signal, and removing a constant DC electric component corresponding to a DC reference light from an electric signal output of the photoelectric conversion means. A signal extraction unit that extracts the modulation detected by the detection unit as an electric signal; a DC component monitoring unit that extracts a DC electric component from the output of the signal extraction unit as a current; and a light emitting unit that emits DC reference light. A current source that generates a current necessary for the current, and a light emission driving unit that adds the current extracted by the DC component monitoring unit and the current generated by the current source, and drives the light emitting unit with the added current. To constitute a sensor circuit.

The photoelectric conversion means is constituted by a photodiode for converting an optical signal into a current signal, and the signal extracting means subtracts a constant DC current component corresponding to DC reference light from the output current of the photodiode. A subtractor, and a current-to-voltage converter for converting a current signal output from the subtractor into a voltage signal. The DC-component monitoring means passes a DC voltage component from an output of the current-to-voltage converter. And a resistor for converting the output voltage of the filter into a current.

Further, the detecting means is characterized in that the detected amount of the object to be measured is a current amount, and modulates the DC reference light according to the strength of the magnetic field generated by the current.

[0010]

In the signal extracting means, a DC electric component corresponding to all DC components of the DC reference light is removed from the electric signal output of the photoelectric conversion means. Therefore, only the modulation component added to the DC reference light by the detection means is extracted from the signal extraction means, and no DC electric component appears in the detection output. Therefore, no DC electric component is extracted from the DC component monitoring means.

On the other hand, when the amount of the DC reference light applied to the detecting means varies, the DC component of the electric signal output from the photoelectric conversion means varies according to the variation in the amount of light. Since the signal extracting unit removes a constant DC electric component from the electric signal output of the photoelectric conversion unit, a DC electric component corresponding to the light quantity fluctuation appears in the detection output of the signal extracting unit. Therefore, the DC component monitoring means outputs a DC electric component corresponding to the light quantity fluctuation as a current. The light emitting means is driven by the addition current of the DC component monitoring means and the respective output currents of the current source, and is driven only by the output current of the current source when there is no light quantity fluctuation. However, when the DC electric component is extracted from the DC component monitoring unit due to the light quantity fluctuation, the light emitting unit is driven by the current obtained by adding the output current of the DC component monitoring unit to the current output from the current source. . Therefore, the light amount of the DC reference light emitted from the light emitting unit to the detecting unit is feedback-controlled to the light amount that cancels the generated light amount fluctuation.

[0012]

Next, an embodiment in which the sensor circuit according to the present invention is applied to a current measuring section of an electronic integrated watt-hour meter will be described.

FIG. 1 is a block diagram showing a configuration of a sensor circuit according to the present embodiment. The LED 11 emits a constant DC reference light shown in the graph of FIG. Here, the horizontal axis of the graph is time, and the vertical axis is the amount of light emitted from the LED 11. This DC reference light propagates through the optical fiber 12 and irradiates the photocurrent sensor 13. The photocurrent sensor 13 is applied with a magnetic field generated by a current flowing through an electric wire drawn into the electronic integrated watt-hour meter. Photocurrent sensor 13
Polarizes the irradiated DC reference light according to the applied magnetic field.
Since the strength of the applied magnetic field changes in proportion to the amount of current flowing through the service wire, the photocurrent sensor 13 applies modulation corresponding to the strength of the applied magnetic field, that is, modulation corresponding to the detected current amount, to the DC reference light. FIG. 2B is a graph showing the DC reference light thus modulated. Here, the horizontal axis of the graph is time, and the vertical axis is the amount of light emitted from the photocurrent sensor 13. As shown in the graph, the added modulation appears as an AC amplitude of the DC reference light, and the modulation component is superimposed as an AC component on the DC component of the DC reference light shown in FIG.

The reference light modulated by the photocurrent sensor 13 is propagated to the photosensor 15 by the optical fiber 14. Photosensor 15 constituting photoelectric conversion means
Is composed of a pin photodiode, and converts the modulated reference light into a current Ip. A current subtraction circuit 16 constituting a subtractor subtracts a constant DC current component Iref from the output current Ip of the photosensor 15. This DC current component I
ref is the DC reference light emitted from the LED 11 in FIG.
This corresponds to the DC component shown in FIG. Current subtraction circuit 16
Is actually performed by adding a current component -Iref to the output current Ip of the photosensor 15. The result of the subtraction is provided to the current / voltage converter 17, and the current signal is converted into a voltage signal. The current subtraction circuit 16 and the current / voltage converter 17 are connected to the photocurrent sensor 1
3 constitutes a signal extracting means for extracting the modulation detected in 3 as an electric signal. The sensing voltage output of the current / voltage converter 17 is provided to a multiplier (not shown), and is multiplied by a voltage value detected by a voltage measuring unit of the electronic integrated watt-hour meter.
The power consumption is calculated.

The output of the current / voltage converter 17 is also supplied to a low-pass filter 18, which outputs the output sensing voltage V of the current / voltage converter 17.
The DC voltage component Voff is extracted from s. D taken out
The C voltage Voff is determined by a resistor 19 constituting a current / voltage converter.
Is converted into a current Ioff. The low-pass filter 18 and the resistor 19 constitute a DC component monitoring unit that extracts a DC electric component from the output of the signal extraction unit as a current. The current I converted by the resistor 19
off is given to the current adder 20. The current adder 20 is also supplied with a constant current I1 generated by the reference light current source 21. The constant current I1 is a current obtained by adjusting the sensing voltage Vs output from the current / voltage converter 17 so that the DC voltage component Voff does not appear when the feedback loop is stabilized.
Is a current required to emit the DC reference light shown in FIG. Here, the current adjustment is performed by adjusting a variable resistor (volume) constituting the reference light current source 21, setting a dip switch, and the like. The current adder 20 constituting the light emission driving means includes a current Ioff output from the resistor 19 and a current I1 output from the reference light current source 21.
And the current obtained by amplifying the added current is
Is driving.

In the sensor circuit according to the present embodiment having such a configuration, as described above, the DC current component Iref corresponding to all DC components of the DC reference light is removed from the output current Ip of the photosensor 15 by the current subtraction circuit 16. Have been. Therefore, the current / voltage converter 17 shown in the graph of FIG.
No DC component appears in the sensing voltage output, and only the modulation component added to the DC reference light by the photocurrent sensor 13 is extracted. Here, the horizontal axis of the graph is time, and the vertical axis is voltage. Therefore, no DC electric component is extracted from the low-pass filter 18, and the current Ioff output from the resistor 19 is zero. That is, LED1
1 is driven only by a constant current I1 generated by the reference light current source 21, and the LED 11 emits a DC reference light having a constant light quantity shown in FIG.

By the way, from the LED 11 to the photocurrent sensor 1
The light amount of the DC reference light applied to the light source 3 may fluctuate. Factors that cause this variation include, for example, LED 11
And aging of the photocurrent sensor 13. LED1
The light emission amount of the photocurrent sensor 1 itself decreases with aging, and the light amount sensed by the photocurrent sensor 13 decreases with aging of the sensor optical element forming the photocurrent sensor 13. Further, when distortion occurs due to bending or the like in the optical fiber 12 that propagates the DC reference light, the distortion may cause a variation in the amount of reference light. That is, when the refractive index of the optical fiber 12 changes due to the distortion, the attenuation of the light propagating through the optical fiber 12 changes with the change in the refractive index, and the amount of light applied to the photocurrent sensor 13 changes.

When such a change occurs in the amount of DC reference light applied to the photocurrent sensor 13, the photosensor 15
Changes in the DC component of the current Ip output from the light source according to the light quantity fluctuation. Since a constant DC current component Iref is removed from the output of the photosensor 15 by the current subtraction circuit 16, a DC voltage component Voff according to the light quantity fluctuation appears in the sensing voltage output of the current / voltage converter 17. Therefore, this DC is controlled by the low-pass filter 18.
The voltage component Voff is taken out, and the resistor 19 outputs a positive or negative DC current Ioff according to the light quantity fluctuation.
Therefore, the output current of the current adder 20 becomes the current I1 + Ioff obtained by adding the current Ioff from the resistor 19 to the constant current I1 generated by the reference light current source 21.
1 is driven by this added current. Therefore, LED
The light amount of the DC reference light emitted from 11 increases or decreases in accordance with the generated light amount fluctuation, and the light amount of the DC reference light irradiated on the photocurrent sensor 13 is adjusted to a constant light amount before the fluctuation. That is, in the sensor circuit according to the present embodiment,
The light amount of the reference light emitted from the LED 11 is feedback-controlled to a light amount that cancels the generated fluctuation, and the photocurrent sensor 13 is always irradiated with a constant light amount of the DC reference light.

The difference between the sensor circuit according to the present embodiment and the conventional sensor circuit can be explained as follows. That is, the LED in the conventional sensor circuit uses the DC current Ioff according to the DC voltage component Voff always appearing in the sensing voltage output as the LED driving current ILED (ILED =
Ioff). However, in the sensor circuit according to the present embodiment, the above-described added current I1 + Ioff is used as the LED drive current (ILED = I1 + Ioff). In order to make the light emission amount of the LED the same in the present embodiment as in the prior art, the ILED must be a constant value in the conventional and the present embodiment. Therefore, in the present embodiment, as described above, the current I
1 to adjust this current I1 to the conventional LED drive current ILE
D and the current Iof output from the resistor 19
f is set to zero to keep the LED drive current ILED at the same current value as before. The current Ioff output from the resistor 19
Is zero, which means that the DC voltage component Voff in the sensing voltage Vs is zero. According to the present embodiment, the DC voltage component Voff conventionally included in the sensing voltage Vs
off is removed.

As described above, in the sensor circuit according to the present embodiment, the DC voltage component Voff does not usually appear in the sensing voltage Vs output from the current / voltage converter 17. Therefore, only the AC signal component detected by the photocurrent sensor 13 is output to the multiplier, and the DC voltage component Voff for driving the LED is not output unlike the related art. Therefore, in this embodiment, the multiplier performs multiplication based on the accurate detection amount, and the power consumption is accurately calculated.

When the light quantity applied to the photocurrent sensor 13 fluctuates, a DC voltage component Voff corresponding to the light quantity fluctuation appears in the sensing voltage Vs, and the DC voltage component Voff stabilizes the feedback loop. It is a small component necessary to make That is, the DC voltage component Voff always appears in the sensing voltage output of the conventional current / voltage converter, and is the DC voltage component Vof for driving the LED.
It is extremely small compared to f. Accordingly, a light amount fluctuation occurs, and a DC voltage component Voff appears in the sensing voltage Vs,
Even if this DC voltage component Voff is output to the multiplier, the weighing error that occurs is insignificant compared to the conventional weighing error. Therefore, according to the sensor circuit according to the present embodiment, the DC voltage is included in the sensing voltage Vs in the low current range of the detection current while maintaining the light amount stability accuracy of the reference light irradiated to the photocurrent sensor 13 as before. Component Voff
Can be greatly reduced.

As described above, according to this embodiment, the offset voltage included in the sensing voltage can be easily reduced to zero with a small number of additional components, while maintaining the target accuracy of the light amount stabilization. For this reason, a sensor circuit that can significantly improve the measurement accuracy of the measured electric energy compared to the conventional one is easily realized, and is suitable for an electronic watt-hour meter that performs current measurement with high accuracy over a wide dynamic range. It is possible to provide a highly accurate current sensor circuit.

In the above embodiment, the case where the present invention is applied to the ammeter side of the electronic integrated watt-hour meter has been described. However, the sensor circuit according to the present invention is not limited to such a current measuring sensor circuit. is not. That is, any sensor circuit having a sensor element that modulates the reference light in accordance with the detection amount may be used, and the measurement target is not necessarily limited to the current amount. Even when the present invention is applied to such sensor circuits having different measurement targets, the same effects as those of the above embodiment can be obtained.

[0024]

As described above, according to the present invention, only the modulated component added to the DC reference light by the detecting means is extracted from the signal extracting means, and the DC electric component appears in the detection output in principle. Absent. Further, when the light amount of the DC reference light applied to the detecting unit fluctuates, a DC electric component appears in the detection output of the signal extracting unit, but this DC electric component is a slight one corresponding to the light amount fluctuation. . Therefore, a sensor circuit with a simple configuration that can accurately measure the detected amount while maintaining the stability accuracy of the amount of light applied to the detecting unit is provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a sensor circuit according to one embodiment of the present invention.

FIG. 2 is a graph showing a signal waveform of each part of the sensor circuit according to the present embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional sensor circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Light emitting diode (LED) 12, 14 ... Optical fiber 13 ... Photocurrent sensor 15 ... Photosensor 16 ... Current subtraction circuit 17 ... Current / voltage converter 18 ... Low pass filter 19 ... Resistor 20 ... Current adder 21 ... Reference Current source for light

Continuation of the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 19/00 G01R 21/00-22/04 G01R 11/00-11/66 G01J 1/02

Claims (3)

(57) [Claims] A light emitting means for emitting a DC reference light; a detecting means for modulating the irradiated DC reference light in accordance with a detection amount; and an optical signal modulated by the detecting means into an electric signal. Photoelectric conversion means for converting, and signal extraction means for removing a constant DC electric component corresponding to the DC reference light from the electric signal output of the photoelectric conversion means and extracting the modulation detected by the detection means as an electric signal; A DC component monitoring unit that extracts a DC electric component as a current from the output of the signal extraction unit, a current source that generates a current necessary for the light emitting unit to emit the DC reference light, and a DC component monitoring unit. A light emission drive unit configured to add the extracted current and the current generated by the current source and drive the light emission unit with the added current. 2. The photoelectric conversion means comprises a photodiode for converting an optical signal into a current signal. The signal extraction means subtracts a constant DC current component corresponding to the DC reference light from an output current of the photodiode. And a current-to-voltage converter that converts a current signal output from the subtractor into a voltage signal, wherein the DC component monitoring means includes a filter that passes a DC voltage component from the output of the current-to-voltage converter. 2. The sensor circuit according to claim 1, further comprising a resistor for converting an output voltage of the filter into a current. 3. The detection amount of the detection means is a current amount,
3. The sensor circuit according to claim 2, wherein a modulation corresponding to a strength of a magnetic field generated by a current is applied to the DC reference light.